A measuring cell of the kind described above is disclosed in British Patent 1,344,616.
The known measuring cell includes an electrolyte chamber accommodating the measuring electrode and the counter electrode. The measuring electrode is applied as an electrically-conductive layer to the back surface of a diffusion membrane facing the electrolyte. The diffusion membrane is protected on the side thereof facing the ambient against mechanical influences by a permeable protective disc. It is necessary to provide an adequately large supply of electrolyte in order that measuring cells of the above-mentioned type are operationally and measurement ready over an adequately long time duration. The charge carriers generated at the boundary interface "electrolyte/measuring electrode/gas sample" diffuse in the electrolyte supply between the measuring electrode and the counter electrode. Accordingly, a good ion mobility is required for an adequate response time for measuring cells of this type to thereby prevent the premature exsiccation or concentration of the electrolyte. This increases the size of such measuring cells so that especially portable measuring apparatus become inconvenient to handle.
Published British patent application 2,094,005 discloses that the electrodes in the form of layers are brought as close to each other as possible. This compact electrode arrangement is however achieved with a complex wick configuration which makes it possible to bring the necessary electrolyte to the surface of the measuring electrode from the electrolyte supply.